As a general rule brushless electric motors have a rotor equipped with permanent magnets, which is rotatably mounted inside a stator carrying a plurality of stator coils. The individual stator coils are for the most part combined by means of winding heads to form multiphase (usually three-phase) stator coil strings which are commutated electrically by means of power conversion electronics. Brushless electric motors are distinguished by a low maintenance requirement and a greater degree of efficiency compared with brushed machines. They are therefore suited in particular for use in electromechanical braking devices, such as wedge brakes for example.
In order to achieve high motor powers with small dimensions the stator coils of the individual stator poles must be implemented as single-tooth windings with a high winding density. In the case of a high winding density, the volume occupied by the empty spaces between the coil wires is minimized, and accordingly the space occupied by the coil wire material—copper as a general rule—is maximized. The proportion of the space occupied by the coil wire material in relation to the total volume of the coil winding is referred to as copper fill factor. In the case of a higher copper fill factor realized by way of a higher winding count, in other words by means of a denser packing of the windings, a greater stator pole field and thus a higher motor torque are obtained with the wire diameter remaining unchanged and with the same coil current, whereby the coil volume is retained unchanged.
The attainable motor torque is not however determined only by way of the copper fill factor of the individual stator poles but also by way of the copper fill factor of the stator arrangement overall. To this end, the stator coils of adjacent stator poles must abut one another as gaplessly as possible, to which end the abutting side faces of the pole teeth, in other words the side faces of the stator coils arranged at the stator poles, must be as flat as possible. This is achieved by means of an orthocyclic winding of the pole teeth, in which the wires of one winding layer are guided into the grooves (in other words the depressions in the surface of a winding layer in the area of two abutting winding wires) of the winding layer situated thereunder in each case. As a result, in cross section the coil winding shows a honeycomb-like hexagonal packing structure, wherein an optimum degree of groove filling (in other words the highest possible copper fill factor) and a flat external delimitation of the winding within half a wire diameter are achieved.
The stator coils used for the pole teeth of the electric motors described above are wound around a coil carrier having a winding former rectangular in cross section, the length of which exceeds its width by several times. In order to obtain an orthocyclic winding as described above also in the case of such types of length-to-width ratios, the winding and layer transitions of a coil winding are in each case undertaken at a front face of the winding former. If the winding transition or layer transition were to come to be located at one of the side faces of the winding former, then this side face would have a prominence and no longer have the requisite flatness for a closely adjacent fitting of the pole teeth.
It has however become apparent that automated orthocyclic winding is not possible in the case of long narrow coil carriers having a rectangular cross section because the winding and layer transitions cannot be forced at the front face of the winding former intended for this. Winding of the coil carriers for narrow stator poles is therefore carried manually at the present time. Mass production tailored to the cost requirements of automobile manufacture is however not possible in this way.